EXCEED THE SPACE PROVIDED. Several large epidemiological studies have associated a profound reduction in the incidence of Alzheimer's Disease (AD) in older individuals who took non-steroidal anti-inflammatory drugs (NSAIDs) for longer than 2 years. However, clinical trials of NSAIDs in patients with established AD failed to show efficacy. This has led to the hypothesis that NSAIDs suppress pathologic processes critical to the initiation of AD and that these processes may be related to inhibition of the cyclooxygenase enzymes and subsequent prostaglandin (PG) production. We propose to test this hypothesis by quantifying endogenous eicosanoid production in subjects enrolled in the Alzheimer's Disease Anti-inflammatory Prevention Trial (ADAPT), an NIA-sponsored study of NSAIDs in the prevention of AD. Specifically, we will 1) determine the efficacy of selective and non- selective NSAIDs t o suppress 1 evels o f quantitative b iomarkers o f P G p reduction systemically and in t he central nervous system of ADAPT participants; 2) determine the efficacy of NSAIDs to suppress levels of quantitative biomarkers of oxidative damage systemically and in the central nervous system of ADAPT participants; and 3) correlate changes in the levels of biomarkers of PG production and oxidative damage with rates of cognitive decline as determined in ADAPT. We have developed highly accurate and precise mass spectrometric assays to quantify PGs, PG metabolites, and lipid peroxidation products and are routinely performing these assays in our laboratory. These studies will provide important insights into the mechanisms by which NSAIDs prevent AD.